Integrated circuits for the most part require reference sources that are to the greatest possible extent independent of process fluctuations, fluctuations in the supply voltage and/or fluctuations of ambient variables. Ambient variables that shall be mentioned here include the temperature, in particular, though vibrations and pressure, for example, should also be regarded as ambient variables.
A large number of circuits and circuit concepts have been disclosed hitherto for generating a reference value, for example, a reference voltage or a reference current. One known method for generating a reference value is the principle of compensating for fluctuations which are accumulated in the form of additive disturbances on the reference value. Primarily bipolar transistors or diodes are provided for this purpose. One method employed in generating a reference value is the principle of temperature compensation. For this purpose, firstly an output variable proportional to temperature is provided in a first circuit unit. Generally such circuits are referred to as “proportional to absolute temperature” (PTAT) circuits. This proportional temperature dependence of the output variable is then compensated for in a further switching unit.
All the methods disclosed hitherto require a sufficiently high supply voltage for suppressing process fluctuations and fluctuations of the supply voltage.